Hey all, we wrote a guide on how to create watch only wallets on Desktops, Android phones, and iPhones.

https://whotookmycrypto.com/watch-only-wallets/

In summary, if you are a Ledger wallet user, you are in luck as they offer options on all platforms (mobile phones and desktops) for creating watch only wallets. If you use other wallets, you may need to consider other options:
1) Desktop -> Electrum
2) iPhone -> bitWallet
3) Android -> Sentinel

Any feedback is appreciated. Thanks!